Buggy code:
public abstract class ClassificationTestBase < T > extends LuceneTestCase { public static final String POLITICS_INPUT = "Here<seq2seq4repair_space>are<seq2seq4repair_space>some<seq2seq4repair_space>interesting<seq2seq4repair_space>questions<seq2seq4repair_space>and<seq2seq4repair_space>answers<seq2seq4repair_space>about<seq2seq4repair_space>Mitt<seq2seq4repair_space>Romney..<seq2seq4repair_space>" + "If<seq2seq4repair_space>you<seq2seq4repair_space>don't<seq2seq4repair_space>know<seq2seq4repair_space>the<seq2seq4repair_space>answer<seq2seq4repair_space>to<seq2seq4repair_space>the<seq2seq4repair_space>question<seq2seq4repair_space>about<seq2seq4repair_space>Mitt<seq2seq4repair_space>Romney,<seq2seq4repair_space>then<seq2seq4repair_space>simply<seq2seq4repair_space>click<seq2seq4repair_space>on<seq2seq4repair_space>the<seq2seq4repair_space>answer<seq2seq4repair_space>below<seq2seq4repair_space>the<seq2seq4repair_space>question<seq2seq4repair_space>section." ; public static final BytesRef POLITICS_RESULT = new BytesRef ( "politics" ) ; public static final String TECHNOLOGY_INPUT = "Much<seq2seq4repair_space>is<seq2seq4repair_space>made<seq2seq4repair_space>of<seq2seq4repair_space>what<seq2seq4repair_space>the<seq2seq4repair_space>likes<seq2seq4repair_space>of<seq2seq4repair_space>Facebook,<seq2seq4repair_space>Google<seq2seq4repair_space>and<seq2seq4repair_space>Apple<seq2seq4repair_space>know<seq2seq4repair_space>about<seq2seq4repair_space>users." + "<seq2seq4repair_space>Truth<seq2seq4repair_space>is,<seq2seq4repair_space>Amazon<seq2seq4repair_space>may<seq2seq4repair_space>know<seq2seq4repair_space>more." ; public static final BytesRef TECHNOLOGY_RESULT = new BytesRef ( "technology" ) ; private RandomIndexWriter indexWriter ; private Directory dir ; private FieldType ft ; String textFieldName ; String categoryFieldName ; String booleanFieldName ; @ Override @ Before public void setUp ( ) throws Exception { } @ Override @ After public void tearDown ( ) throws Exception { super . tearDown ( ) ; <START_BUG> indexWriter . close ( ) ; <END_BUG> dir . close ( ) ; } protected void checkCorrectClassification ( Classifier < T > classifier , String inputDoc , T expectedResult , Analyzer analyzer , String textFieldName , String classFieldName ) throws Exception { } protected void checkCorrectClassification ( Classifier < T > classifier , String inputDoc , T expectedResult , Analyzer analyzer , String textFieldName , String classFieldName , Query query ) throws Exception { } protected void checkOnlineClassification ( Classifier < T > classifier , String inputDoc , T expectedResult , Analyzer analyzer , String textFieldName , String classFieldName ) throws Exception { } protected void checkOnlineClassification ( Classifier < T > classifier , String inputDoc , T expectedResult , Analyzer analyzer , String textFieldName , String classFieldName , Query query ) throws Exception { } private void populateSampleIndex ( Analyzer analyzer ) throws IOException { } protected void checkPerformance ( Classifier < T > classifier , Analyzer analyzer , String classFieldName ) throws Exception { } private void populatePerformanceIndex ( Analyzer analyzer ) throws IOException { } private String createRandomString ( Random random ) { } private void updateSampleIndex ( Analyzer analyzer ) throws Exception { } }

Fix:
indexWriter . shutdown ( ) ;